Diabroticine beetles are a significant problem during the growth of, inter alia, corn (field, pop, seed, and sweet), beans, Cucurbitaceae (including cucumbers, melons, squash, and pumpkins), peanuts, peas, potatoes, and sweet potatoes. Corn is conveniently used to describe the effects of diabroticine beetles. These pests are the direct or indirect (i.e., as a vector for bacteria and inoculation of melons and squash) cause of millions of dollars of crop and garden damage annually. Damage by these beetles has continued despite over 30 years of attempts at control.
Diabroticine beetles encompass multivoltine and univoltine species. Multivoltine species (e.g., the southern corn rootworm) can produce up to 3 generations a year. Univoltine species (e.g., northern and western corn rootworm) have a life cycle that starts with eggs laid 4-24 inches below the soil surface in the Fall. In early Spring and over the course of several weeks, the larvae (a form of immature beetle) hatch and begin to feed on nearby roots thereby destroying the root's anchoring abilities and the microhairs responsible for mineral, nutrients, and water assimilation. If the plant roots have not been so damaged that the plants falls over, the yield from the affected plants is reduced due to impaired nutrition.
After feeding, the diabroticine larvae pupate and emerge from the ground as adult beetles. Univoltine beetles emerge at some time during mid July through August (depending on local climate). Male diabroticine beetles emerge about 1 week before the females (week 1) which, in turn, emerge at about the same time as corn silks emerge. Because the fresh silks emit a number of volatile agents which are attractive to both the male and female beetles, the 7-10 days of silking represents a period of high-feeding activity for the beetles. The beetles immediately begin to migrate up the stalk toward the leaves, ears, and silks. This compulsion is quite strong since there is evidence that the beetles will not move down the corn stalk in response to attractants. Throughout this period, the beetles feed and mate.
The key to control of the diabroticine beetles is to disrupt the life cycle by affecting the immature and/or adult beetles. One method known in the art as "banding" refers to the practice of trying to control the larvae by applying a contact insecticide in or along a furrow containing planted seeds. The theory behind banding is that larvae will enter the treated area when searching for room and die due to contact with the insecticide.
Unfortunately, microbial attack impairs the efficacy of insecticides in the soil well before all the larvae have had time to hatch and enter the treated band. Concerns for groundwater contamination, the impact on nontarget organisms (e.g., bird kill), and the hazards of human exposure to the toxic insecticides all restrict the use of soil insecticides that might be capable of surviving in the soil through the larval feeding stage.
The effectiveness of banding is also limited by the plants themselves. Plant roots often extend well beyond the treated band leaving the roots vulnerable to attack.
It has been proposed to use the tissue of dried gourds from the Cucurbitale order in combination with 0.01-10% by weight (wt. %) of an insecticide to make a lethal bait for the control of diabroticine beetles. Due to genetic evolution, corn rootworm larvae have evolved to compulsively feed on cucurbitacins.
From Canadian Patent No. 1,195,922, the bitter tasting cucurbitacins in the gourd tissue acts as a compulsive feeding stimulant for diabroticine beetles but does not harm beneficial insects. By coating the gourd tissues with an insecticide, it was intended that the beetles would compulsively consume a lethal quantity of insecticide.
Unfortunately, it is difficult and expensive to grow cucurbitale order crops with high cucurbitacin concentrations. Hybrid species must be located or selected to provide even a marginal level of cucurbitacins.
Also proposed in Lush U.S. Pat. No. 4,992,275 is the use of 3-6 mm pellets containing an active insecticide and whole, dried, ground, raw sweet corn. The bait is taught as useful for controlling corn rootworm larvae as well as cutworms, wireworms, billbugs, seed corn maggots, grabs, lesser corn stalk borer, seed corn beetle, flea beetles, European and Southwestern corn borer, fire ants and other ant species, onion maggots, sweet potato weevils, and root maggots, among other types of chewing insects that feed on a variety of plants. Although it is broadly disclosed that "binders for holding the bait particles together" (column 2, lines 3-4) may be used, other passages teach that natural sweet corn is sufficiently high in oil and sugar that added oils and sugars are unnecessary (column 7, lines 20-27). In addition, rain or winds is taught to remove the bait from the treated zone necessitating retreatment (column 4, lines 33-36).
It would be desirable to have a bait formulation that used safe, inexpensive ingredients with a high level of efficacy against immature and mature diabroticine even when applied through conventional spraying equipment in aqueous solution as well as when applied as a dry granular bait.